1. Field of the Invention
The present invention relates to a lens support frame which can be incorporated in an optical apparatus such as a camera.
2. Description of the Related Art
FIGS. 7 and 8 show a lens support frame 100 and three lens elements (a first lens element 107, a second lens element 108 and a third lens element 109), which are fixed to the inside of the lens support frame 100, that are provided as components of a lens barrel (photographic lens) of a compact digital camera.
The lens support frame 100 is provided, on an inner peripheral surface thereof, with a first lens holding groove 101, a second lens holding groove 102 and a third lens holding groove 103 which are formed as annular grooves and arranged in the forward/rearward direction. The first lens holding groove 101 is greater in diameter than the second lens holding groove 102, and the front ends of the first lens holding groove 101 and the second lens holding groove 102 are open. The third lens holding groove 103 is smaller in diameter than the second lens holding groove 102, and the rear end of third lens holding groove 103 is open.
Three lens-centering depressions 104 that are arc shaped as viewed from the front are formed on an inner peripheral surface of the first lens holding groove 101 at equi-angular intervals in a circumferential direction as portions depressed (recessed) radially outwards (double-headed arrows A shown in FIG. 7 show the formation areas of the lens-centering depressions 104). The front end of each lens-centering depression 104 is open and the rear end of each lens-centering recess 104 is closed.
In addition, three first lens-bonding depressions 105 that are arc shaped as viewed from the front are formed on an inner peripheral surface of the first lens holding groove 101 as portions recessed radially outwards. The first lens-bonding depressions 105 are formed at equi-angular intervals in a circumferential direction (double-headed arrows B shown in FIG. 7 show the formation areas of the first lens-bonding depressions 105), and the circumferential positions of the first lens-bonding depressions 105 are different from those of the lens-centering depressions 104 (namely, the first lens-bonding depressions 105 are not aligned with the lens-centering depressions 104 in the axial direction of the lens support frame 100, respectively). The front end of each first lens-bonding depression 105 is open and the rear end of each first lens-bonding recess 105 is closed.
Three second lens-bonding depressions 106 that are arc shaped as viewed from the front are formed on an inner peripheral surface of the second lens holding groove 102 at equi-angular intervals in a circumferential direction as portions recessed radially outwards (double-headed arrows C shown in FIG. 7 show the formation areas of the second lens-bonding depressions 106). The front end of each second lens-bonding depression 106 is open and the rear end of each second lens-bonding recess 106 is closed. As shown in the drawings, the three second lens-bonding depressions 106 are positioned immediately behind the three first lens-bonding depressions 105, respectively (namely, the circumferential positions of the three second lens-bonding depressions 106 are coincident with those of the three first lens-bonding depressions 105 as viewed from the front).
The second lens element 108, which is substantially identical in diameter to the second lens holding groove 102, is fixed to the second lens holding groove 102 by positioning the rim of the second lens element 108 in the second lens holding groove 102 from the front, thereafter injecting an adhesive into each second lens-bonding depression 106 from the front (from the front-end opening thereof), and curing the adhesive adhered to both the rim of the second lens element 108 and the inner surface of each second lens-bonding depression 106.
The first lens element 107, which is substantially identical in diameter to the first lens holding groove 101, is fixed to the first lens holding groove 101 after the second lens element 108 is fixed to the second lens holding groove 102. More specifically, after an operation to center the first lens element 107 is performed with a lens-centering tool (not shown) that is inserted into the lens-centering depressions 104 from the front (through the front-end openings of the lens-centering depressions 104) following an insertion of the rim of the first lens element 107 into the first lens holding groove 101 from the front, the first lens element 107 is fixed to the first lens holding groove 101 by injecting an adhesive into each first lens-bonding depression 105 from the front (from the front-end opening thereof) and curing the adhesive that is adhered to both the rim of the first lens element 107 and the inner surface of each first lens-bonding depression 105.
The third lens element 109, which is substantially identical in diameter to the third lens holding groove 103, is fixed to the third lens holding groove 103 by positioning the rim of the third lens element 109 in the third lens holding groove 103 from the rear, and thereafter thermally caulking the perimeter of the third lens holding groove 103 against the rim of the third lens element 109.
An example of the related art is disclosed in Japanese Patent Publication No. 3,442,507.
In general, the injection amount of adhesive into each first lens-bonding depression 105 and each second lens-bonding depression 106 is not so large as to completely fill the lens-bonding depressions 105 and 106, but is an amount (small amount) which fills only a part of the space of each lens-bonding depression 105 and 106. Therefore, even after the adhesive is cured (solidified), a void remains in a part of each lens-bonding depression 105 and 106.
Accordingly, in the case where the three second lens-bonding depressions 106 are positioned immediately behind the first lens-bonding depressions 105, respectively, like in the case of the lens support frame 100, the possibility of minute particles such as dust which have entered the first lens holding groove 101 from the front of the first lens element 107 through each of the three first lens-bonding depressions 105 entering in between the rear surface of the first lens element 107 and the front surface of the second lens element 108 through each of the three second lens-bonding depressions 106 that are respectively positioned immediately behind the three first lens-bonding depressions 105 increases.
If a large quantity of adhesive enough to fill the entire part of each second lens-bonding depression 106 is injected into each second lens-bonding depression 106 and is cured, each second lens-bonding depression 106 is completely filled with cured adhesive (since the second lens holding grooves 102 which do not have the three second lens-bonding depressions 106 are formed), so that dust can be prevented from entering in between the rear surface of the first lens element 107 and the front surface of the second lens element 108 through the three second lens-bonding depressions 106.
However, since gas is generated when an adhesive cures, the gas generated from the adhesive is trapped inside the space between the rear surface of the first lens element 107 and the front surface of the second lens element 108, thus causing the first lens element 107 and the second lens element 108 to fog if each second lens-bonding depression 106 is totally filled with adhesive. Accordingly, it is not preferable that an adhesive be injected into the entire part of each second lens-bonding depression 106.